Method of folding plastic sheet material



Nov. 8, 1949 R. F. TABER METHOD OF FOLDING PLASTIC SHEETMATERIAL 3 Sheets-Sheet l Flled Feb. 6, 1947 Nov. 8,. 1949 R. F. TABER 2,487,494

METHOD OF FOLDING PLASTIC SHEET MATERIAL Filed Feb. 6, 1947 v 5 Sheets-Sheet 2 gwuem tom 4 Ral h E Taber Nov. 8, 1949 R. F. TABER 2,487,494

METHOD OF FOLDING PLASTIC SHEET MATERIAL I Filed Feb. 6, 1947 3 Sheets-Sheet 3 Fig". 6 .34 34 38 38 k 38 J9 39 I 39 grwawfo'o RaZ vh F Taber Patented Nov. 8, 1949 NlTED STATES PATENT ()FFICE METHOD OF FOLDING PLASTIC SHEET MATERIAL Ralph F. Taber, Bliff'al'o, N. Y. Application February 6, 1947, Serial No. 726,916 4 Claims. (01. 1s56) This invention relates to a method for forming permanent folds in plastic sheet material.

The invention provides an economical and rapid method of forming folds in plastic sheet material with the use of heat for softening the plastic material in the portion being folded so that it will be folded-into a permanent bend for thereafter effectively retaining its shape.

With the present method, a plastic sheet to be folded is placed in position for support on a pair of spaced parallel ledges. Then, a heated folding blade is moved to engage the edge with the portion of the sheet between the ledges. The blade is then moved to bend the sheet about the blade between the ledges with sufficient slowness in movement of the blade to allow the heat to soften the material at the portions engaged with the blade. The sheet material becomes readily folded I to provide a bend portion at the blade that will take a permanent set after removal of the heated blade therefrom. With this method, a permanent fold of any degree may be made in plastic material. Where it is desired to have the portions of the sheet on opposite sides of the fold lie in substantial contact with one another, the invention provides for movement of the spaced parallel supporting portions or ledges, in the form of supporting bars, toward one another. This moves the "ends of the sheet at opposite sides of the blade extending from the fold portion en'- g-aging the corners of the heated forming blade into adjacent but spaced relation to the sides of the forming blade. Then, the forming blade is withdrawn while the folded sheet is held be.- tween the bars. The bars are moved closer together after withdrawal of the blade from the fold to bend the fold portion of the sheet to bring and hold the portions at opposite sides of the fold in close contact while at the same time absorbing the heat in the plastic sheet to cool and set the bend therein.

In the drawings:

Fig. 1 shows in substantially diagrammatic form the left-hand 'upper side portions of a machine to form folds in plastic sheet material according to the method 'of the invention.

Fig. 2 is a substantially diagrammatic View showing the right-hand side of the machine, with portions broken away for convenience in illustration.

Fig. 3 is a plan view of the machine, as shown in Figs. 1 and 2, Withportions broken away and shown in section to illustrate some of the details of construction.

Fig. 4 is an enlarged diagrammatic cross s'e'c- 2 tion with a portion of a sheet in position ready to be folded according to the invention.

Fig. 5 is a diagrammatic cross-section showing how the folding blade illustrated in Fig. 4 is moved to fold the sheet with the ends extending at right angles from the fold portion in accordance with the invention.

Fig. 6 is a fragmentary cross-section showing how the folding blade is moved into position to engage a sheet to be folded in its supported position ona pair of spaced parallel fold forming bars providing spaced ledges between which the sheet is bent in the folding operation.

Fig. 7 shows a cross-section similar to Fig. 6 with the folding blade moved into a position between the fold forming bars to bend the sheet to be folded with the ends at opposite sides of the fol-ding blade extending substantially at right angles.

Fig. 8 shows how the folding blade is moved from the position of Fig. '7 downwardly an additional amount between the fold forming bars, illustrating another step in the operation of forming a tight fold in a plastic sheet. 4

Fig. 9 illustrates a further operation progressing from Fig. 8 in the folding of a sheet to provide a tight fold therein, with the blade at the bottom of its stroke of movement.

Fig. 10 is a view similar to Fig. 9 showing still another progressive position forming a fold in a sheet wherein the parallel forming bars are in the same position as shown in Figs. 8 and 9, while the folding blade has been partially removed from the fold in the sheet which remains in position between the bars, as shown in Fig. 9.

Fig. 11 illustrates the final folding position of the fold forming bars and the blade in which the blade has been removed from between the bars and the fold in the sheet while the bars have been moved closer together to'bri-ng the portions of the sheet at opposite sides of the fold therein into close engagement with one another between the fold forming bars while the bars engage the fold portion of the sheet to absorb the heat therein and set the fold during further movement of the blade away from the bars.

Fig. 12 illustrates a sheet having a finished tight fold formed therein.

The method provided by the present invention is preferably carried out by a suitable machine providing the ledges or fold forming bars and the folding blade so that the ledges or bars may be arranged and maintained at the desired spaced relation and moved toward one another when a tight fold is to be formed, and also to provide for 3 the movement of the blade at the desired speed into a predetermined position with respect to the forming ledges or bars to secure the folding of a series of sheets uniformly.

The machine is illustrated in substantially diagrammatic form and will preferably be constructed in accordance with the disclosure in the co-pending application filed on even date herewith entitled Plastic sheet folding machine.

The machine hasa suitable base i carrying a rigid supporting frame 2 formed with a fiat sheet supporting top portion 3, depending side walls 4 and front wall portion 5. Front wall portion 5 extends downwardly from the front edge of top portion 3 and has a downwardly and forwardly inclined portion terminating in a horizontal forwardly extending portion so arranged that the top portion of rigid supporting frame 2 is offset to the rear of the bottom front portion thereof. At the juncture between front wall portion ti and sheet supporting top portion 3, the supporting frame is formed with a seat to support a fold-forming bar 6 with the upper face in coplanar relation with top portion 3. A similar fold-forming bar l is supported in opposed relation to fold-forming bar 8 on carrier 8 having a sheet-supporting top portion 9 formed with depending side members it. Side members it are located beyond opposite sides of frame 2 and have the lower ends mounted on shaft H extending through side walls 4 for rotatably supporting carrier 8 on supporting frame 2.

Side members it at the right-hand side of the machine, as shown in Fig. 2, is provided with a rearwardly extending portion carrying an eccentrically mounted roller l2 engaged with the periphery of cam 63 on cam shaft M. Cam shaft M is rotatably mounted in side walls t of supporting frame 2. A ratchet wheel i5 is mounted on the opposite end of cam shaft l4 beyond lefthand side wall 4. A pair of pawl-carrying plates iii are rotatably mounted at one end on cam shaft is between ratchet wheel l5 and side wall i, as shown in Fig. 1, and carry spring-pressed pawls H on their free ends arranged to engage the teeth on ratchet wheel l5.

An operating shaft I8 is rotatably mounted at opposite ends in the lower front portions of sides 3 on supporting frame 2. A pair of actuating levers it and '28 are mounted on the left and right-hand ends respectively, of shaft l8, as shown in Figs. 1 and 2, while an operating lever 2i has; the upper end secured to the central portion thereof between side walls l and extends downwardly under the front portion of supporting frame 2. Foot pedals 22 are mounted on the lower end of operating lever 2i. Operating lever 2? has a rearwardly extending rod .23 mounted in the upper end thereof, as shown in Fig. 2, carryin a counter-weight 2 5 on the rear end. A dash pot 25 has the piston rod 26 thereof connected at one end to counter weight 26 and the rear end of rod 23, while the lower end of cylinder is mounted on a suitable bracket 28 carried by base i.

A pair of links 28 are pivotally secured to the rear end of actuating lever 59, Fig. 1. Each link has its opposite end pivotally connected to the fr e end of pawl-carrying plate 56. This provir. s for the simultaneous movement of both pawl-carrying plates in opposite directio .s relaive to each other about cam shaft M whenever actuating lever i9 is moved to operate links 29 in manner that will be hereinafter described.

A pair of spaced parallel blade-carrying arms 3d are provided with an eccentric mounting on a blade-supporting shaft 3! supporting frame 2 and rotatably mounted in side walls l thereof. Blade-carrying arms 30 are mounted on the free ends of shaft 38 outwardly beyond side walls 4 in the manner clearly shown in Figs. 1 to 3.

Blade-carrying arms 36 extend forwardly and upwardly from shaft 3| to a position above supporting frame 2 at the front portion thereof, where they carry folding blade assembly 32. The folding blade assembly extends transversely between the .free upper ends of arms 30 and has a body portion 33 constructed to receive a suitable conventional electric heating element for heating body on in order to transmit heat to folding blade 38 with the provision of suitable controls for maintaining a desired uniform heat. Arms 39 mount the folding blade assembly with folding blade 34 positioned to engage between fold-forming bars 6 and '1, respectively. Links 35 are pivotally connected to the forward ends of actuating levers l9 and 263 and at the opposite ends to the respective blade-carrying arms 36, as shown in Figs. 1 and 2. Set screws 35 on the lower forward ends of actuating levers l9 and 233 respectively, are adjusted to engage the 'upper end of base i in the movement of operating lever 2i rearwardly for limiting the extent to which folding blade 3 extends downwardly between fold-forming bars 5 and 'i. A set screw 3'! is mounted on the rear lower side of actuating lever id, as shown in Fig. l for engaging the upper end of base i and limiting the forward movement of operating lever 2i and the upward movement of blade-carrying arms 3t and folding blade 34.

Each fold-forming bar has the side opposed to the other bar formed with a longitudinally extending groove throughout the central portion thereof, indicated at 387 Each groove has bottom portions 3) arranged in angular relation at opposite sides of the grooves so that a resilient strip til may have one edge seated and secured in one side of the groove while the opposite edge or margin projects slightly outwardly from the groove at the other side in spaced angular relation to the bottom of the groove, as clearly shown in Figs. 6 to 11.. The free edges of resilient strips all project outwardly from groove 33 beyond the face of the respective folding bars 5 and l to provide resilient gripping cooperation in the 0ppos-ed relation of bars 6 and I to engage opposite sides of a folded sheet and hold it between the bars. The eccentric mounting for arms 30 may be adjusted to vary the position of folding blade t l relative to bars 6 and I depending upon the spaced relation of the bars 6 and. 1 obtained by adjusting eccentrically mounted roller l2. These adjustments are made for sheets of varying thickness as well as to change the closeness with which folding bars 6 and l are arranged in the different folding positions. the folding operation may be accurately controlled to secure the desired result.

In folding sheets according to the method of the present invention, a plastic sheet of the desired thickness and size is engaged on top portions 9 and 3 respectively, with one edge in contact with the gauge bar t! to position the portion to be folded in the central portion between bars 6 and 1. Gauge bar 4! is mounted on top portion for adjustment toward and from folding bar 6 so that it may be set for gauging the position of the fold in each sheet to be formed.

If it is desired to form a fold or bend in extending through By this means a. sheet of plasticv materiaL. reference to Figs. 4 and 5.. illustrates how this may be obtained by moving the sheet upv against a gauge bar 4|. Figs. 4 and 5 illustrate a forming bar 42 formed with a. V-shaped groove or chamber 43. in the upper face thereof. This bar 42. may be substituted for folding bars 6. and where it is desired. to form a right-angle bend in the plastic; sheet material. In folding a sheet in the use ofjforming bar 42, it will be understood thatit is held in a stationary position with respectto. top supporting portion 3.0f frame member 2; through renderingspring-pressed pawls. inoperative relative to. ratchet. wheel [5. Bar 42 forms a stationary forming bar for cooperation with, heated folding sheet while it is bent about the blade between theledges on bar-42; As folding blade ismoved downwardly toward the bottom of groove 43 toflexthe sheet between the ledges, the heat at the edge of the blade will be absorbed by the plastic sheet material as it is gradually bent downwardly until the bottom-ofgroove 43 is reached, as shown in Fig. 5. This gives the sheet material time to absorb sufiicient heat to soften the material so that it will flow into bent orcurved relation about the edge of heated blade 34v without stressing the structure of the sheet. Blade 34 is moved downwardly until the lower edge normally engages the sheet in the bottom of V-shaped groove 4-3 and forming bar- 42 sothat a right-angle bend in the sheet is formed, as shown in Fig. 5.

In forming the right-angle bend as shown in Figs; i and 5, operating lever 2| will bemoved from the forward position to rearward position determined by the position of blade 34, as shown in Fig. 5 where it is engaged at the bottom of groove 43. Then the operating lever is releasedv so that counter-weight 24 will move it back to the starting position as shown in Fig. 2, with a decelerated movement governed by dash pot 2.5. This will give an opportunity for blade 34 to move from the folded portion of the sheet engaged in V shaped groove43, as shownin Fig. 5. and allow theheat in the sheet tobe absorbed by folding bar 42 so that the plastic material in the sheet will become set in the folded position by the time folding blade 34 reaches its uppermost position whereupon the completed folded sheet is removed from forming bar 42.

If desired, a right-angular bend may be formed in a sheet of plastic material through the. use of forming-bars 6 and By this method a sheet isinserted against gauge bar 4| so that the portion desired to be folded is placed in the proper position between bars 6 and l. as shown Fig. 6. Then, operating lever 2| is moved to bring folded blade 34 downwardly to engage the sheet, as shown in Fig. 6 and bend it downwardly into the chamber between bars 6 and 1 to the position shown in=Fig. '7. This method of folding a sheet maybeobtained by adjusting screws 35 to limit the movement of actuating levers l9 and 26 so which the sheet to be folded will.

that the position. of blade 34' between bars 6, and is limited; to: extend d wnw rdly between bar 6. and I: to! no. greater extent than that shown in Fig. 7. The sheet is flexed as, the folding blade. 34 moves from the position shown: in Fig. 6 downwardly to the position shown in Fig. '7. As..- the blade; moves from the position of Fig. 6 to, that shown in; Fig. 7; the sheet will absorb sufficient heat for securing the permanent. folding; of: the sheet with. the portions at opposite sides of the. blade extending in right-angular relation, the: sameas: that shown in Fig. 5.. The blade isheld for a short; period sufficient to allow the plastic material in the sheet to heat. and permanently set the sheet in folded unstressed position, as shown in Fig. 7', whereupon it may be withdrawn and the sheet allowed to remain engaged between bars 6 and 1 until it cools and sets the material.

The invention also provides. a, method of form-- ing a tight fold in a sheet in the manner shown inFigs. 6 to 11 inclusive. The sheet is first placed against gauge bar 4| so that the portion to be folded is centered; in position over bars 6- and I. Screws 36 are adjusted; to control the amount blade: 3.4.- extends. between bars 6 and 1. Then, folding blade 34 is moved downwardly to engage the sheet in the position shown in Fig. 6. Blade iidshasqit's downward movement continued. to bend the sheet into the position shown. in Fig. 7 during which time the heat from the blade is transmitted .to the sheet to soften the materialthereof sothat it will readily fold about the blade. The down;- wardmovement ofthe folding blade is continued from the position shown in Fig. While the rier with folding bar l has been moved. inwardly slightly from its initial position by the rotation of cam shaft 4 and cam l3: in a counter-clockwise direction, as shown in Fig. 2. Rotation of cam l3. disengages dwell 441 from roller |2 and moves cam portions 45 into engagement with roller l2 thereby.- moving bar slightly closer to bar 6. This motion of, bar closer to bar 6 is obtained when the parts are in the position shown in Fig.

I 6 and the position of bar I, as illustrated in Fig.

'7 is the same. Heated blade 34. as shown in Figs. 6.to 11; is square on the edge so that plastic sheets will bend about-the blade to engage only the cor-- ners. The plastic sheet being folded will be heated in the region engaged with the corners of the blade /34' along opposite side faces.

Heated blade 34: is then moved still farther downwardly between fold. forming bars 6 and I where; a position illustrated in Fig. 8' is reached while-the plastic sheet is further heated. Fold forming bars 6 and: l remain in substantially the same position, as shown in Fig. 7 during this further movement of heated folding blade 34. The movement of blade 34. continues to the position shown in Fig; 9 where the lower edge of the blade extends slightly below the lower edges of channels 38 so that the fold. portion in the sheet is located below. thelower ends of resilient strips 40.

From the position of Fig. 9; folding blade 34. is gradually withdrawn from'thefolded' sheet between fol-d forming bars 6 and I. Fig. 10 illustrates the partial withdrawal of folding blade-34 from the folded sheet held in the same position shown in Fig. 9 between fold forming-bars 6 and I through the cooperation of resilient strips 40' with the folded sheet.

As folding blade 34- is further withdrawn from engagement with the sheet and frombetween bars 6. and 1, fold forming bar I is moved still closer to bar 6. Bars 6 and 1 bend the fold portion of the sheet below the resilient strips for moving the portions of the sheet at opposite sides of the fold into close contact with one another, as shown in Fig. 11. During the withdrawal of blade 34 from the fold portion in the sheet, bars 6 and l in the position shown in Fig. 11 hold the folded sheet for a sufficient length of time to absorb the heat from the fold portion and adjacent portions thereof to thereby cool the plastic material so that it will permanently set in a tight folded position. The movement of fold forming bars 6 and 1 into the close position shown in Fig. 11 is obtained by a cam lobe 46 on cam l3 engaging roller l2 for rocking carrier 8 in moving bar 1 toward bar 6.

When folding blade 34 reaches the position shown in Fig. 9, operating lever H has reached its rearmost position of movement by manual operation so that set screws 36 and 3'! engage the frame to limit further movement. Operating lever 2! then moves forwardly under the operation of counter-weight 24 and the control of dash pot 25 at a predetermined slow rate until the starting position shown in Fig. 2 is reached. This slow withdrawal of blade 3 from the fold in the sheet, as shown in Fig. 9, to the position shown in Figs. 10 and 11, secures an efiicient timing of the folding operation so that the sheet is fully folded into the tight position with the material in the sheet being formed to follow the direction of the fold so as to maintain a permanent set in the material after it cools.

When blade 34' has reached its starting position and operating lever 2! is in the position shown in 2, another dwell 44 in cam l3 moves into position to receive roller l2 so that as the starting position is reached, roller l2 seats in the next dwell A l and fold-forming bar 1' moves to the spaced position shown in dot-anddash lines in Fig. 6 to release the folded sheet. The folded sheet is then discharged from between bars 6 and l and has an appearance in end elevation similar to that shown in Fig. 12.

This method of folding plastic sheet material secures an efficient and economical folding operation in which folding blade 34 is moved rather rapidly into engagement with a sheet to bend it between bars 5 and 1 in spaced relation. Then,

with a rapidly decelerating motion of folding F blade 34, the heat softens the plastic sheet material so that the sheet may be readily folded due to subsequent cooperation of fold-forming bars 6 and l with blade 34 in the manner above described. The decelerated or slow movement of F J folding blade 34 during the forming of the fold in the sheet is timed to give the heat sufiicient opportunity to soften the material of the sheet throughout the fold portion to permanently form the material of the sheet into the folded position.

The invention claimed is:

1. The method of folding plastic sheet material consisting in supporting a sheet on a pair of spaced parallel heat absorbing ledges over a folding chamber with the portion to be folded located midway between said ledges, moving a heated folding blade laterally to the plane of said ledges and sheet to engage said sheet portion to be folded to start the heating of said sheet portion and slowly moving saidsheet portion while continuing the heating thereof to soften the material in said sheet portion sufficiently to bend around said heated blade edge into said folding chamber into a folded position about said blade while supported by said ledges, retracting said folding blade from said folded sheet as soon as heated portions of said sheet engage said ledges while said ledges cooperate to support said folded sheet and rapidly absorb the heat from said sheet to permanently set the fold in said sheet portion, and then removing the sheet from said ledges and chamber.

2. The method of folding plastic sheet material consisting in supporting a sheet on a pair of spaced parallel fold-forming bars, moving a heated folding blade to engage said sheet midway between said bars to start heating of a narrow strip portion of said sheet and slowly moving the portion engaged by said blade while continuing heating of said strip portion with the blade between said bars to form a fold in said sheet about said blade while supported by said bars as rapidly as the heat softens the material in said strip portion sufiiciently to bend about said blade, moving said bars toward said blade to additionally fold said sheet about the blade and grip said folded sheet while said blade continues heating said strip portion and said bars begin absorbing the heat from said sheet, withdrawing said blade from the fold in said sheet and from between said bars, moving said bars still closer together during: the withdrawing of said blade to hold and further fold said sheet and for rapidly absorbing the heat in said sheet and cooling said folded sheet to cause said strip portion to permanently set in folded shape after withdrawal of said blade, and finally moving said bars apart and removing the completed folded sheet therefrom.

3. The method of folding plastic sheet material consisting in supporting a sheet on a pair of spaced parallel heat absorbing fold-forming bars, providing sheet gripping means in association with sai bars, moving a heated folding blade to engage and start heating a strip portion of said sheet between said bars and slowly moving the central portion of said sheet therewith between said bars while continuing the heating of said strip portion to soften the material sufiiciently to bend said sheet about said blade therebetween,

maintaining said blade in sheet-folding position for a limited time between said bars sufiicient to heat the material in said sheet to form a permanent fold therein about said blade, moving said bars and sheet gripping means toward one another at opposite sides of said folded sheet to additionally fold said sheet about said blade and to grip and hold said sheet in said gripping means, withdrawing said blade from the fold in said sheet and from between said bars, moving said bars still closer together to more fully engage said bars to tightly fold said sheet and rapidly absorb the heat in said sheet to cool the sheet for permanently setting the fold, and subsequently moving said bars apart into the original spaced parallel relation to release said gripping means and bars from said sheet and removing said folded sheet therefrom.

4. The method of folding plastic sheet material consisting in supporting a sheet along spaced parallel portions thereof moving a heated folding blade to engage a narrow edge thereof with a narrow strip portion at the central portion of said sheet between said spaced parallel supported portions for cooperation therewith to fold said sheet at said narrow strip portion, maintaining said blade with only said narrow edge engaged with said narrow strip portion a limited time sufficient to heat said strip portion to soften the To material in said strip portion sufiiciently to bend,

slowly moving said blade while continuing heating of said strip portion to form it into a fold at the edge of said blade while continuing to support said sheet at said spaced parallel portions, withdrawing said blade from said folded sheet after said blade has completely folded said sheet and more fully engaged said folded sheet between said supporting portions without engaging said sheet during withdrawal while said sheet remains supported at said spaced parallel portions for rapid absorption of heat thereby cooling of the fold formed in said narrow strip portion while maintained in spaced relation to said blade, and finally removing said folded sheet after cooling of said fold portion from support along said spaced parallel portions.

, RALPH F. TABER.

REFERENCES CITED The following references are of record in the file of this patent:

5 UNITED STATES PATENTS Number Name Date Re. 21,479 Trabucco June 4, 1940 503,292 Niedringhaus et a1. Aug. 15, 1893 10 1,006,911 Cook Oct. 24, 1911 2,114,621 Bergstein Apr. 19, 1938 2,339,304 Von Haase Jan. 18, 1944 2,431,353 Vamer et al Nov. 25, 1947 

